Home Chemistry Element Hydrogen


What is Hydrogen?

Hydrogen is the only chemical element in the periodic table in which the valence electron is under the direct influence of the nucleus or there is no shielding electron. It has the symbol ‘H‘ and the molecular formula H2.  The hydrogen molecule is a colorless, odorless, tasteless, flammable gas which used in the earliest time for the production of water.

Hydrogen element symbol, properties, and isotopes protium, deuterium, and tritium

Hydrogen has three isotopes having the chemical name protium (1H1), deuterium (1H2), and tritium (1H3). The atom of hydrogen element has a very simple structural model. It contains one electron and one proton with atomic number = 1 and atomic weight or mass = 1.007829.

Under ordinary conditions, due to the presence of one valence electron in the 1s-orbital, it forms a wide number of common chemical bonding such as covalent, ionic, bridge bonds, and hydrogen bonding.

Where is Hydrogen Found?

In 1766 Henry Cavendish, an English chemist and physicist discovered the most combustible element or molecule hydrogen. The name hydrogen was given from the origin of Greek words meaning ‘water maker’.

Besides the common physical state of matter like solid, liquid, and gas in the Earth’s universe, H2 is a gas molecule at room temperature. It is the third most abundant chemical element after oxygen and silicon and 2nd most abundant gas molecule after oxygen.

Position of Hydrogen in Periodic Table

The ns1 electronic configuration justifies the position in period-1 and group-1 with the alkali metals family (lithium, sodium, potassium, rubidium, cesium, and francium). The ionization energy of hydrogen is also similar to that of alkali metals.

position of hydrogen in periodic table

If we consider the electron configuration of hydrogen, it is just one electron short of the next noble gas element helium. Therefore, it may be placed in group 17 with the halogen family such as fluorine, chlorine, bromine, and iodine. All these elements have very high electronegativity and electron affinity.

Due to the presence of the half-filled valence electrons, it is also placed in group 14 with the carbon family. Therefore, it forms a wide number of covalent molecules with a wide range of polarity.

Oxidation State of Hydrogen

The most common oxidation number of hydrogen element = +1, but due to unique characteristics, it also shows a −1 oxidation state.

For example, in lithium hydride (LiH), sodium hydride (NaH), Cesium hydride (CsH), and calcium hydride (CaH2), the oxidation state or number of hydrogen = −1.

Isotopes of Hydrogen

Hydrogen has three isotopes having the chemical names protium, deuterium, and tritium. The chemical formulas of these isotopes are 1H1, 1H2, and 1H3 respectively.

These three isotopes form three covalent gas molecules like dihydrogen, dideuterium, and ditritium. These isotopes are used as an alternative fuel for engines or renewable energy sources for our environment.

Hydrogen Properties

Symbol H
Discovery Henry Cavendish in 1766
Name derived from The Greek words hydro and genes, meaning water forming
Allotrope H2
Common isotope 1H2 (deuterium), 1H3 (tritium)
Crystal structure Hexagonal crystal lattice
Periodic properties
Atomic number 1
Electron per shell 1
Atomic weight 1.008
Electronic configuration 1s1
Group 1
Period 1
Block s-block
Physical properties
State at 20 °C Gas
Melting point −259.16 °C, −434.49 °F, 13.99 K
Boiling Point −252.88 °C, −423.18 °F, 20.27 K
Density 0.000082 g cm−3
Chemical properties
Atomic radius (non-bonded) 1.10 Å
Covalent radius 0.32 Å
Oxidation number or states 1, −1
Ionization energy 1st: 1312.05 kJ mol−1
Electron affinity 72.769 kJ mol−1
Electronegativity 2.19 (Pauling scale)
Molar heat capacity
 28.836 J mol-1 K-1
CAS number 133-74-0

Facts About Hydrogen

H2 is a very stable and nonreactive species due to high bond energy but the atomic form is the most reactive species. Only one percent of atomic forms are present in the H2 gas molecule.

The half-life of the atomic form is nearly 1 second at 0.2 mm pressure. A huge specific heat (432.6 kJ mol−1) is used for the recombination of atomic H. This process is used for high-temperature welding of tantalum and tungsten metals.

Due to high reactivity, it functions as a strong reducing agent. It reduces different types of common chemical compounds like ethylene, acetylene, hydrogen peroxide, and metal ions.

Hydrogen Element in the Atmosphere

Hydrogen is a unique type of chemical element that is not found free in the earth’s atmosphere but is widely used in everyday life. The kinetic energy of H2 molecules at the earth’s temperature is sufficient to escape from the earth’s gravitational energy. Therefore, the density of H2 decreases in our environment.

Hydrogen Spectrum

Hydrogen atoms absorb energy to shift their valence electrons particles to different energy levels. The electrons in higher energy levels are relatively unstable and hence drop back to the lower energy level to produce the electromagnetic spectrum or H-spectrum.

Nuclear Spin Isomers

When the nucleus of an atom contains an odd number of nucleons, the nucleus has a resultant spin. If such two atoms combine to form a diatomic molecule, the nuclei may have their spin parallel or anti-parallel. It is called nuclear spin isomerism.

  1. The molecule in which the two nuclei have a parallel spin is called an ortho-isomer.
  2. The molecule with antiparallel nuclear spins is called a para-isomer.

Such nuclear spin isomer is found in H2, D2, T2, N2, O2, etc. The conversion of para-H2 to the ortho-H2 compound is normally very slow. They involved the forbidden transition between two energy states of the different spin municipalities.

What is Hydrogen Used for?

Elemental Hydrogen and its compounds are widely used in the different types of fuel cells and industrial production processes. The most common uses of hydrogen are given below,

Industrial Uses

  • It is used for the manufacture of ammonia.
  • It is an important chemical compound used for the manufacturing of hydrochloric acid, sulfuric acid, nitric acid, methyl alcohol, etc.
  • Atomic hydrogen torches are used for welding of high melting metals like tantalum and tungsten.
  • It is also used for the reduction of metal oxides. A direct reduction of iron ore by H2 is used for the manufacturing of iron.
  • The liquid H2 molecule is used in the propulsion of rockets.
  • In bubble chambers, liquid hydrogen is used to study high-energy particles.
  • Hydrogen oxygen type mixture is used in the fuel cells for the production of renewable energy which uses widely electric vehicles.

Laboratory Uses

  • In a hydroformylation reaction, H2 may add a formyl group into alkenes. The produced formyl compound subsequently changed to form different types of alcohol. These alcohols are used for the preparation of PVC resin and detergents.
  • Methyl alcohol prepared from hydrogen is subsequently oxidized by the oxo process to form formaldehyde which is a starting material for the synthesis of plastics.
  • Hydrogen electrodes are used for the determination of the pH of an unknown solution.
  • The hydrogen spectrum is used to analyze different types of physical or chemical properties.

Uses of deuterium

  • Deuterium is a common isotope of chemical element hydrogen which is used mainly for the production of heavy water.
  • The heavy water used as a moderator and coolant in nuclear power reactors is obtained commonly from deuterium molecules.
  • Deuterium oxide is the main source of deuterium compounds.
  • To study the reaction mechanisms, we widely use deuterium and its compounds.

Uses of tritium

  • Tritium is widely used as a tracer element due to its radioactivity.
  • Tritium extensively uses hydrological studies on the moment of groundwater in the earth’s environment
  • It is also used to study the absorption of crystalline metals and multiphase alloys in autoradiography.
  • The hydrogen isotope tritium is used to study the reaction mechanism, reaction kinetics, and homogeneous catalysis.